Communication apparatus, server, communication system, and communication method

ABSTRACT

According to one aspect, a communication apparatus is provided which is on a LAN and coupled to a server via an external network involving a NAT traversal with a router of the LAN. The communication apparatus is configured to determine a configuration of the router of the LAN; and request the server to transmit a NAT update request packet to the router, which is registered in the server and performs the NAT traversal, when it is determined that the configuration of the router of the LAN is in two or more stages.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of International Application No.PCT/JP2014/061477, filed on Apr. 23, 2014, the entire contents of whichare incorporated herein by reference.

FIELD

The present disclosure is related to a communication apparatus, aserver, a communication system, and a communication method.

BACKGROUND

Japanese Laid-open Patent Publication No. 2005-102316 and JapaneseLaid-open Patent Publication No. 2005-130453 disclose a configuration inwhich apparatuses on LAN (Local Area Network) at home are coupled toapparatuses on Internet via a router.

Addressing systems allocated to the networks differ between theapparatus on the LAN and the apparatuses on the Internet. The routerperforms an address conversion by using a NAT entry associating aprivate IP address of the LAN and a global IP address of the Internet,which enables communications (i.e., NAT traversal) between theapparatuses on the LAN and the apparatuses on the Internet.

Techniques related to the NAT traversal includes, for example, a portforwarding with a static NAT/UPnP (Universal Plug and Play) and adynamic NAT/STUN (Simple Traversal of UDP through NATs). The portforwarding with the static NAT/UPnP sets a fixed NAT entry with respectto a NAT router, or sets a fixed port forward with UPnP with respect toan UPnP-capable router. The dynamic NAT dynamically generates the NATentry at the communication via the Internet. In this case, the NAT entryis deleted upon no communication being performed for a certain time.

However, after the NAT entry has been deleted, the IP addresses cannotbe associated in the router, which disables the communication betweenthe apparatuses on the LAN and the apparatuses on the Internet.

On the other hand, the NAT entry set by the UPnP-capable router is notdeleted. However, the UPnP technique cannot be used in the apparatus andits neighboring router on the LAN.

SUMMARY

According to one aspect, a communication apparatus is provided which ison a LAN and coupled to a server via an external network involving a NATtraversal with a router of the LAN. The communication apparatus isconfigured to determine a configuration of the router of the LAN; andrequest the server to transmit a NAT update request packet to therouter, which is registered in the server and performs the NATtraversal, when it is determined that the configuration of the router ofthe LAN is in two or more stages.

The object and advantages of the embodiment will be realized andattained by means of the elements and combinations particularly pointedout in the claims. It is to be understood that both the foregoinggeneral description and the following detailed description are exemplaryand explanatory and are not restrictive of the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are diagrams illustrating a communication systemaccording to a first embodiment.

FIG. 2 is a diagram illustrating a NAT traversal in a case where arouter of the communication system is in a single stage.

FIG. 3 is a diagram illustrating a NAT traversal in a case where arouter of the communication system is in multiple stages.

FIG. 4 is a diagram illustrating a function configuration of a PC, aserver, and a router according to the first embodiment.

FIG. 5 is a flowchart of a NAT entry update process (in a single-stagerouter configuration).

FIG. 6 is a diagram illustrating an example of a LAN registrationrequest in S1 in FIG. 5.

FIG. 7 is a flowchart of a LAN registration request reception process inS2 in FIG. 5.

FIG. 8 is a diagram illustrating an example of a LAN registrationrequest in S3 in FIG. 5.

FIG. 9 is a diagram illustrating an example of a LAN registrationrequest transmitted from the PC in S4 in FIG. 5.

FIG. 10 is a diagram illustrating an example of the NAT entry stored inS5 in FIG. 5.

FIG. 11 is a diagram illustrating an example of a LAN registrationrequest after a NAT conversion in S6 in FIG. 5.

FIG. 12 is a flowchart of a LAN registration request reception processin S8 in FIG. 5.

FIG. 13 is a diagram illustrating an example of a LAN information tablein S8 in FIG. 5.

FIG. 14 is a flowchart of a LAN update request transmission process inS9 in FIG. 5.

FIG. 15 is a diagram illustrating an example of a NAT update requesttransmitted from the server in S11 in FIG. 5.

FIG. 16 is a diagram illustrating an example of a NAT update requestafter a NAT conversion in S13 in FIG. 5.

FIG. 17 is a flowchart of a NAT update request reception process in S15in FIG. 5.

FIG. 18 is a flowchart of a NAT entry update process according to thefirst embodiment (in a single-stage or multiple-stage routerconfiguration).

FIG. 19 is a flowchart of a LAN registration request reception processin S22 in FIG. 18.

FIG. 20 is a diagram illustrating an example of a LAN configurationdetermination request in S23 in FIG. 18.

FIG. 21 is a flowchart of a LAN configuration determination requestreception process in S24 in FIG. 18.

FIG. 22 is a flowchart of a LAN configuration determination process inS30 in FIG. 18.

FIG. 23 is a diagram illustrating an example of a LAN configurationdetermination response in S31 in FIG. 18.

FIG. 24 is a flowchart of a LAN configuration determination responsereception process in S32 in FIG. 18.

FIG. 25 is a diagram illustrating a communication system according to asecond embodiment.

FIG. 26 is a diagram illustrating a function configuration of a PC, aserver, and a router according to the second embodiment.

FIG. 27 is a flowchart of a NAT update cycle optimization processaccording to the second embodiment.

FIG. 28 is a diagram illustrating an example of a LAN registrationrequest in S41 in FIG. 27.

FIG. 29 is a diagram illustrating an example of a LAN registrationrequest transmitted from the PC in S44 in FIG. 27.

FIG. 30 is a flowchart of a LAN registration request reception processin S48 in FIG. 27.

FIG. 31 is a diagram illustrating an example of a cycle optimizationrequest in S50 in FIG. 27.

FIG. 32 is a flowchart of a cycle optimization request reception processin S52 in FIG. 27.

FIG. 33 is a diagram illustrating an example of a cycle transmissionmanagement table (at the time of an initial registration) in S52 in FIG.27.

FIG. 34 is a flowchart of a NAT entry survival confirmation transmissionprocess in S54 in FIG. 27.

FIG. 35 is a diagram illustrating an example of a NAT entry survivalconfirmation in S55 in FIG. 27.

FIG. 36 is a flowchart of a NAT entry survival confirmation transmissionprocess in S54 in FIG. 27.

FIG. 37 is a diagram illustrating an example of a NAT entry survivalconfirmation response in S61 in FIG. 27.

FIG. 38 is a flowchart of a cycle transmission timer update process (atthe time of the NAT entry survival confirmation response reception) inS71 in FIG. 27.

FIG. 39 is a diagram illustrating an example of a cycle transmissionmanagement table in S71 in FIG. 27.

FIG. 40 is a flowchart of a response waiting timer time-out process inS78 in FIG. 27.

FIG. 41 is a diagram illustrating an example of a cycle optimizationresponse in S79 in FIG. 27.

FIG. 42 is a flowchart of a cycle optimization response receptionprocess in S80 in FIG. 27.

FIG. 43 is a diagram illustrating a communication system according to athird embodiment.

FIG. 44 is a diagram illustrating a function configuration of a PC, aserver, and a router according to the third embodiment.

FIG. 45 is a flowchart of a LAN change process according to the thirdembodiment.

FIG. 46 is a diagram illustrating an example of an overlapped LAN searchrequest in S90 in FIG. 45.

FIG. 47 is a flowchart of an overlapped LAN search process in S91 inFIG. 45.

FIG. 48 is a diagram illustrating an example of an overlap managementtable in S91 in FIG. 45.

FIG. 49 is a diagram illustrating an example of an overlapped LAN searchresponse in S92 in FIG. 45.

FIG. 50 is a flowchart of a LAN registration process in S93 in FIG. 45.

FIG. 51 is a diagram illustrating an example of a LAN information tablestored in the server (NAT control part) in S93 in FIG. 45.

FIG. 52 is a diagram illustrating an example of an overlap managementtable in S102 in FIG. 45.

FIG. 53 is a diagram illustrating an example of a LAN information tablein S104 in FIG. 45.

FIG. 54 is a diagram illustrating a hardware resource configuration of aPC, a server, and a router according to the first through thirdembodiments.

DESCRIPTION OF EMBODIMENTS

In the following, embodiments will be described by referring to theaccompanying drawings. It is noted that elements that have substantiallythe same functional configuration are given the same reference number inthe specification and the drawings, and redundant explanation thereof isomitted.

First Embodiment

At first, a communication system according to a first embodiment of apresent invention is described with reference to FIGS. 1A and 1B. FIGS.1A and 1B are diagrams illustrating the communication system accordingto the first embodiment. FIG. 1A illustrates a case where a routerconfiguration of a LAN of the communication system 10 is in a singlestage, and FIG. 1B illustrates another case where a router configurationof a LAN of the communication system 10 is in multiple stages (two ormore stages).

According to the communication system 10 illustrated in FIG. 1A, a PC 1and a server 2 are coupled to each other via a LAN 11, a WAN 12, andInternet 13. A router 3 a generates a NAT entry in which a private IPaddress of the PC 1 and a global IP address of the WAN 12 are associatedwith each other, and performs an address conversion between the privateIP address and the global IP address based on the NAT entry. In thefollowing, the private IP address is also referred to as “a local IPaddress”. With this arrangement, the communication between the PC 1 andthe server 2 is enabled. It is noted that the WAN 12 and the Internet 13are examples of an external network.

The communication system 10 illustrated in FIG. 1B illustrates a casewhere a router configuration of the LAN 11 is in two stages such thatrouters 3 a and 3 b (also collectively referred to as “a router 3”,hereinafter) are provided. The router 3 b generates the NAT entryassociating the private IP address in the LAN to perform the addressconversion. The router 3 a generates the NAT entry associating theprivate IP address in the LAN 11 with the global IP address of the WAN12 to perform the address conversion.

As illustrated in FIG. 2, the PC 1 transmits an acquisition request ofthe IP address to the neighboring router 3 (i.e., the router 3 b in thecase of a single stage, and the router 3 a in the case of the twostages) (see (1) in FIG. 2). The PC 1 obtains the IP address from theneighboring router 3 (see (2) in FIG. 2).

The PC 1 performs a determination, based on the obtained IP address,whether the router configuration in the LAN 11 is in a single stage ormultiple stages. The PC 1, when determining that the IP address is theprivate IP address, determines that the router configuration of therouter 3 is in the multiple stages, and determines that the conversionfrom the private IP address to the global IP address is performed atanother router ahead of the neighboring router.

On the other hand, the PC 1, when determining that the IP address is theglobal IP address, determines that the router configuration of therouter 3 is in a single stage because it can be determined that theconversion from the private IP address to the global IP address isperformed at the neighboring router.

The router configuration of the router 3 in the LAN 11 is in a singlestage, the NAT traversal can be implemented with the port forwarding bythe UPnP. In this case, the NAT entry is not deleted even if nocommunication is performed for a predetermined time.

If the router configuration of the router 3 in the LAN 11 is in multiplestages, the router 3 on the side of the WAN 12 (i.e., adjacent to theInternet 13) dynamically generates the NAT entry when the communicationwith the Internet 13 is performed. In this case, the NAT entry isdeleted upon no communication being performed for a predetermined time.

According to the communication system 10 of the embodiment describedhereinafter, it is determined the router configuration of the router 3is in multiple stages, and when it is determined that the routerconfiguration of the router 3 is in multiple stages, the PC 1 outputs aregistration request for the LAN 11 (i.e., the registration request forextending the life of the NAT entry even upon no communication for thepredetermined time), and the server 2 transmits a NAT update requestpacket to the registered LAN 11. With this arrangement, it becomespossible to prevent the NAT entry from being deleted even upon nocommunication for the predetermined time.

Specifically, as illustrated in FIG. 3, the PC 1 transmits the LANregistration request to the server 2 when the PC 1 determines that therouter configuration of the router 3 in the LAN 11 is in multiple stages(see (1) in FIG. 3). The router 3 b performs an IP address and portconversion to generate the NAT entry (see (2) in FIG. 3). The router 3 aperforms an IP address and port conversion to generate the NAT entry(see (2)′ in FIG. 3). With this arrangement, the NAT traversal isenabled.

The server 2, in response to the LAN registration request from the PC 1,stores the global IP address and the port information of the PC 1related to (2)′ in a LAN information table described hereinafter (see(3) in FIG. 3). Next, the server 2 transmits the NAT update requestpacket to the global IP address and the port information stored in theLAN information table related to (3) at a predetermined interval(regularly, for example) (see (4) in FIG. 3). When the router 3 areceives the NAT update request packet, the deletion of the NAT entrydue to no communication for the predetermined time is prevented, whichenables keeping a state in which the NAT traversal is enabled (see (5)in FIG. 3). Further, the PC 1 transmits the registration request of theLAN 11 only when the router configuration of the router 3 in the LAN 11is in multiple stages, and the server 2 transmits the NAT update requestpacket in response to the registration request. With this arrangement,if the router configuration of the router 3 is in single stage, the NATupdate request packet is not transmitted periodically, which enablesdecreasing the load of the server 2 and the network.

It is noted that the router 3 b performs the private IP addressconversion to transmit the NAT update request packet to the PC 1. Therouter 3 b, like the router 3 a, can extend the life of the NAT entrywhen the router 3 receives the NAT update request packet (see (5) inFIG. 3).

As described above, according to the embodiment, if the routerconfiguration of the router 3 in the LAN 11 is in multiple stages, theserver 2 transmits the NAT update request packet with UDP (User DatagramProtocol) to the PC 1 related to the global IP address and the portinformation with the predetermined interval, which enables keeping theNAT entry of the router 3.

Next, function configurations of the PC 1, the server 2, and the router3 according to the first embodiment are described. FIG. 4 is a diagramillustrating a function configuration of the PC 1, the server 2, and therouter 3 according to the first embodiment.

The PC 1 includes an UI part 14, a LAN registration part 15, a LANconfiguration determination part 16, an UPnP acquisition part 17, and acommunication control part 18. The PC 1 is an example of ancommunication apparatus on the LAN that performs the NAT traversal withthe router 3 of the LAN 11 to be coupled to the server 2 via an externalnetwork such as Internet 13, etc. The communication apparatus is notlimited to the PC 1. The communication apparatus may be a televisionreceiver, a recording/reproducing apparatus, a game apparatus, amultimedia apparatus such as a music reproducing apparatus, homeappliances with a communication function, such as a refrigerator, awashing machine, an air conditioner, a microwave oven, etc., a portableapparatus, a tablet type terminal, etc.

The UI part 14 includes an interface function for performing the LANregistration to the server 2. The LAN registration part 15 controls theLAN registration to the server 2. The UPnP acquisition part 17 accessesto the UPnP-capable router 3 to obtain the IP address. The LANconfiguration determination part 16 determines, based on the obtained IPaddress, whether the router configuration in the LAN 11 is in singlestage or multiple stages. The communication control part 18 controls thecommunication with other apparatuses with TCP/IP (TCP: TransmissionControl Protocol, IP: Internet Protocol).

The router 3 includes a communication control part 31 and an UPnPprocess part 33. The communication control part 31 controls thecommunication with other apparatuses with TCP/IP. The UPnP process part33 transmits the outward IP address of the PC 1 in response to the IPaddress acquisition by the UPnP acquisition part 17 of the PC 1. Thecommunication control part 31 holds a NAT table 32. The NAT table 32 isa table used for the address conversion and has the NAT entry storedtherein for performing the IP address conversion between the LAN and theWAN 12 (i.e., the Internet 13).

The server 2 includes a communication control part 21, a NAT controlpart 22, and a storage 23. The communication control part 21 controlsthe communication with other apparatuses with TCP/IP. The NAT controlpart 22 transmits the NAT update request packet to the router 3 inresponse to the LAN registration request from the PC 1. The storage 23stores, in a LAN information table 24, information of the NAT entry ofthe router 3 to which the NAT update request packet is to be transmittedin response to the LAN registration request.

Next, a NAT entry update process in the case where the routerconfiguration is in a single stage is explained with reference to FIG.5. FIG. 5 is a flowchart of a NAT entry update process (in asingle-stage router configuration). In FIG. 5, the LAN registrationprocess is performed, and then the NAT entry update process isperformed.

When the NAT entry update process is started, at first, the UI part 14of the PC 1 transmits the LAN registration request (step S1). FIG. 6 isa diagram illustrating an example of information included in the LANregistration request in which a parameter on an upper side and a settingvalue for the parameter on a lower side are illustrated. In the LANregistration request, “LAN registration request” is set in a messagetype 61, and “800 sec” is set in periodical transmission intervalinformation 62.

In FIG. 5 the LAN registration part 15 performs a LAN registrationrequest reception process in response to the LAN registration request ofstep S1 (step S2). According to the LAN registration request receptionprocess in FIG. 7, the LAN registration part 15 determines a terminal ID(step S100), and transmits the LAN registration request to thecommunication control part 18 (step S101). The terminal ID may be a MACaddress of the PC 1, or other IDs that can be uniquely identified on theInternet.

In FIG. 5, then, the LAN registration part 15 transmits the LANregistration request (step S3). As illustrated in FIG. 8, informationincluded in the LAN registration request transmitted from the LANregistration part 15 has the terminal ID 63 “12345” added to the LANregistration request transmitted from the UI part 14 in step S1.

In FIG. 5, then, the LAN registration part 18 transmits an IP packet ofthe LAN registration request (step S4). The IP packet of the LANregistration request illustrated in FIG. 9 is transmitted from the PC 1to the router 3. In the IP packet of the LAN registration request, an IPheader includes a destination IP address 71 and a sender IP address 72set therein, a UDP header includes a destination port 73 and a senderport 74 set therein, and LAN information includes a message type 75, aterminal ID 76, and periodical transmission interval information 77 settherein. In this case, the IP address “100.100.100.1” of the server 2 isset in the destination IP address 71, the IP address “192.168.10.1” ofthe PC 1 is set in the sender IP address 72, the port “2000” of theserver 2 is set in the destination port 73, and the port “1000” of thePC 1 is set in the sender port 74.

In FIG. 5, then, the communication control part 31 of the router 3generates the NAT entry associating the private IP address with theglobal IP address to perform the address conversion (step S5). Asillustrated in FIG. 10, the NAT entry generated by the router 3 includesinformation of a private IP address 81, a private port 82, a global IPaddress 83, a global port 84, a server IP address 85, and a server port86. The NAT entry thus generated is stored in the NAT table 32. Therouter 3 performs, based on the NAT entry, the address conversion fromthe private IP address “192.168.10.1” to the global IP address“120.120.120.120” of the Internet. In this way, the PC 1 performs theNAT traversal, and becomes capable of coupling to the server 2 via theInternet 13.

In FIG. 5, then, the communication control part 31 of the router 3transmits the IP packet of the LAN registration request after the NATconversion to the server 2 (step S6). According to the LAN registrationrequest after the NAT conversion illustrated in FIG. 11, the global IPaddress after the address conversion “120.120.120.120” is set in asender IP address 92, and the global port “1500” is set in a sender port94.

In FIG. 5, then, the communication control part 21 of the server 2receives the IP packet of the LAN registration request after the NATconversion, and transmits the LAN registration request to the NATcontrol part 22 (step S7). The NAT control part 22 performs the LANregistration request reception process (step S8). As illustrated in FIG.12, in the LAN registration request reception process, the NAT controlpart 22 generates the LAN information table 24 (step S103). The storage23 stores the LAN information table 24. The LAN information table 24includes information of a terminal ID 241, a terminal IP address 242, aterminal port number 243, and periodical transmission intervalinformation 244, as illustrated in FIG. 13. An ID for identifying the PC1 is set in the terminal ID 241, the global IP address of the NAT entryis set in the terminal IP address 242, and the global port is set in theterminal port number 243. “800 sec” is set in the periodicaltransmission interval information 244 as a predetermined interval(cycle) at which the NAT update request packet is to be transmitted fromthe server 2 to the router 3 that performs the NAT traversal.

In FIG. 5, then, the NAT control part 22 performs the NAT update requesttransmission process (step S9). As illustrated in FIG. 14, according tothe NAT update request transmission process, the NAT control part 22counts time with a NAT entry update timer, and transmits the NAT updaterequest (step S107) at a lapse of 800 sec, which is periodicaltransmission interval, from the transmission timing of the previous NATupdate request packet. The NAT control part 22 starts counting for thetransmission of the next NAT update request packet with the NAT entryupdate timer (step S108).

In this way, In FIG. 5, the NAT control part 22 transmits the NAT updaterequest (step S10). Then, the communication control part 21 transmitsthe IP packet of the NAT update request to the router 3 (step S11).According to the NAT update request packet illustrated in FIG. 15, adestination IP address 101 and a sender IP address 102 are set in an IPheader, a destination port 103 and a sender port 104 are set in a UDPheader, and a message type 105 and a terminal ID 106 are set in contentof message. The global IP address “120.120.120.120” is set in thedestination IP address 101, and the IP address “100.100.100.1” of theserver 2 is set in the sender IP address 102. Further, the global port“1500” is set in the destination port 103, and the port “2000” of theserver 2 is set in the sender port 104. The message type 105 is “NATupdate”, and the terminal ID 106 is “12345”.

In FIG. 5, then, the communication control part 31 of the router 3 aupdates the NAT entry, and performs the address conversion from theglobal IP address to the private IP address (step S12). Then, thecommunication control part 31 transmits the IP packet of the NAT updaterequest to the PC 1 (step S13). According to the IP packet of the NATupdate request after the NAT conversion illustrated in FIG. 16, theprivate IP address “192.168.10.1” after the address conversion is set inthe destination IP address 111, and the private port “1000” is set inthe destination port 103.

In FIG. 5, then, the communication control part 18 of the PC 1 transmitsthe NAT update request (step S14). The LAN registration part 15 performsthe NAT update request reception process in response to the NAT updaterequest (step S15). At that time, the NAT entry of the router 3 has beenupdated, there is no need for the PC 1 to perform any process.Therefore, illustrated in FIG. 17, in the NAT update request receptionprocess, the LAN registration part 15 does nothing or performs an errorcheck based on the received IP packet (step S109). For example, the LANregistration part 15 may check the terminal ID (see 116 in FIG. 16)included in the IP packet, and output an error display when the terminalID different from that of the own PC is set.

Next, a NAT entry update process in the case where the routerconfiguration is in a single stage or multiple stages is explained withreference to FIG. 18. FIG. 18 is a flowchart of a NAT entry updateprocess (in a single-stage or multiple-stage router configuration). InFIG. 18, the LAN registration process is performed, and then the NATentry update process is performed. In the LAN registration process, aLAN configuration determination process is performed. In FIG. 18, therouter 3 b closest to the PC 1 and illustrated in FIG. 1B is illustratedas the router 3.

At first, the UI part 14 of the PC 1 transmits the LAN registrationrequest (step S21). Then, the LAN registration part 15 performs the LANregistration request reception process (step S22). According to the LANregistration request reception process in FIG. 19, the LAN registrationpart 15 determines a terminal ID (step S110), and transmits a LANconfiguration determination request to the LAN configurationdetermination part 16 (step S111).

Accordingly, in step S23 illustrated in FIG. 18, the LAN configurationdetermination request is transmitted from the LAN registration part 15to the LAN configuration determination part 16. In FIG. 20, an exampleof the LAN configuration determination request in which the message type121 is set to the LAN configuration determination request.

In FIG. 18, then, the LAN configuration determination part 16 performs aLAN configuration determination request reception process (step S24).According to the LAN configuration determination request receptionprocess illustrated in FIG. 21, the LAN configuration determination part16 determines whether the UPnP function of the PC 1 is effective (stepS113). If the LAN configuration determination part 16 determines thatthe UPnP function of the PC 1 is effective, the LAN configurationdetermination part 16 transmits an acquisition request of an IP address(also referred to as “an outward address” hereinafter) to the UPnPacquisition part 17. If the LAN configuration determination part 16determines that the UPnP function of the PC 1 is not effective, the LANconfiguration determination part 16 transmits the response, whichrepresents that the result of the LAN configuration determination is“undeterminable”, to the LAN registration part 15.

In FIG. 18, then, the UPnP acquisition part 17 performs an outwardaddress acquisition request reception process (step S26) in response tothe acquisition request of the outward address of step (step S25). Then,the UPnP acquisition part 17 transmits the IP packet of the outwardaddress acquisition request to the UPnP process part 33 of the router 3b adjacent to the PC 1 (step S27). The UPnP process part 33 transmits anIP packet for reporting the outward address (step S28).

Then, the UPnP acquisition part 17 transmits the acquisition response ofthe outward address (step S29). The LAN configuration determination part16 performs the LAN configuration determination process (step S30).According to the LAN configuration determination process illustrated inFIG. 22, the LAN configuration determination part 16 determines theoutward address (i.e., the network address) obtained from the router 3closest to the PC 1 (step S117). If the LAN configuration determinationpart 16 determines that the obtained outward address is the global IPaddress, the LAN configuration determination part 16 determine that therouter configuration is in a single stage such that the conversion tothe global IP address is performed at the router 3 closest to the PC 1.Correspondingly, the LAN configuration determination part 16 transmitsthe response, which represents the determination result “single stage”of the router configuration of the LAN, to the LAN registration part 15(step S118).

On the other hand, in step S117, the LAN configuration determinationpart 16 determines that the outward address is the private IP address,the LAN configuration determination part 16 determines that the LAN 11includes another router that performs the conversion from the private IPaddress to the global IP address. Correspondingly, the LAN configurationdetermination part 16 determines that the router configuration in theLAN 11 is in multiple stages. Thus, the LAN configuration determinationpart 16 transmits the response, which represents the result “multiplestage (two or more stages)” of the LAN configuration determination, tothe LAN registration part 15 (step S119).

In FIG. 18, then, the LAN registration part 15 receives the response ofLAN configuration determination (step S31). According to an example ofthe LAN configuration determination response illustrated in FIG. 23,“LAN configuration determination response” is set in a message type 123,and “single stage/multiple stages/undeterminable” is set in resultinformation 124.

In FIG. 18, then, the LAN registration part 15 performs a LANconfiguration determination response reception process (step S32).According to the LAN configuration determination response receptionprocess illustrated in FIG. 24, the LAN registration part 15 determinesthe result of LAN configuration determination response (step S121). Ifthe LAN registration part 15 determines that the router configuration isin a single stage, the LAN registration part 15 determines that the NATentry is not to be deleted even upon no communication for thepredetermined time. Thus, the LAN registration part 15 determines thatthe transmission of the NAT update request packet from the server 2 isnot necessary and thus does nothing (step S122). On the other hand, ifthe LAN registration part 15 determines that the router configuration isin multiple stages, the LAN registration part 15 transmits the LANregistration request to the communication control part 18 (step S123).It is noted that the periodical transmission process of the NAT updaterequest packet by the server 2 in response to the LAN registrationrequest is performed as described above with reference to step S3through step S15 illustrated in FIG. 15, thus the explanation thereof isomitted.

Thus, according to the embodiment, the PC 1 determines the routerconfiguration in the LAN 11, and if the PC 1 determines that the routerconfiguration is in multiple stages, the PC 1 transmits the LANregistration request to the server 2. The server 2 periodicallytransmits the IP address of the NAT update request at a predeterminedinterval (5 sec, for example) in response to the LAN registrationrequest. With this arrangement, even if the router configuration in theLAN 11 is in multiple stages, it becomes possible to prevent thedeletion of the NAT entry upon no communication for a predeterminedtime.

As described above, according to the communication system 10 of thefirst embodiment, because the PC 1 determines the router configurationof the LAN to which the PC 1 is coupled, the PC 1 can determine whetherthe periodical transmission of the IP packet of the NAT update requestfrom the server 2 is necessary. Thus, even if the router configurationis in multiple stages, it becomes possible to have the NAT entrycontinuously stored in the router, which enables keeping a state inwhich the NAT traversal can be performed. It is noted that, in the caseof the single-stage router configuration, it is configured such that theNAT entry set by the router whose UPnP function is effective is notdeleted. Therefore, if it is determined that the router configuration isin single stage, the PC 1 does not transmit the LAN registrationrequest, and thus the NAT update request packet is not transmitted fromthe server 2. As a result of this, it becomes possible to reduce theload of the server 2 as well as traffic of the network.

Second Embodiment

Next, an overall configuration and a function configuration of acommunication system 10 according to a second embodiment of the presentinvention is explained with reference to FIG. 25 and FIG. 26. FIG. 25 isa diagram illustrating the communication system 10 according to thesecond embodiment. FIG. 26 is a diagram illustrating a functionconfiguration of a PC 1, a server 2, and a router 3 according to thesecond embodiment. The second embodiment differs from the firstembodiment in that there is a transmission interval optimization server7 in addition to the server 2. It is noted that, in FIG. 25, a routerconfiguration of the router 3 (router 3 a) is in a single stage;however, the router configuration may be in multiple stage.

As illustrated in FIG. 26, a function configuration of the PC 1, theserver 2, and the router 3 are the same as that according to the firstembodiment. The transmission interval optimization server 7 addedaccording to the second embodiment includes an cycle optimization part25 and a communication control part 26. The cycle optimization part 25controls the transmission interval of the NAT update request packet. Thecycle optimization part 25 stores, in a cycle transmission managementtable 27, information for controlling the transmission interval of theNAT update request packet. The communication control part 26 controlsthe communication with other apparatuses with TCP/IP.

Next, a NAT update cycle optimization process according to theembodiment is explained with reference to FIG. 27. FIG. 27 is aflowchart illustrating the NAT update cycle optimization process. InFIG. 27, the LAN registration process and the NAT entry update processaccording to the first embodiment are performed in the server 2, and theNAT update cycle optimization process of the NAT update request packetis performed in the transmission interval optimization server 7.

When the NAT update cycle optimization process is started, at first, theUI part 14 of the PC 1 transmits the LAN registration request (stepS41). As illustrated in FIG. 28, according to an example of informationincluded in the LAN registration request, “LAN registration request” isset in a message type 126, “800 sec” is set in periodical transmissioninterval information 127, and “YES” is set in optimization information128. The parameter of the optimization information 128 is set to “YES”,if a user checks a box “optimization” on the screen of the UI part 14,for example.

The LAN registration part 15 generates the LAN registration request(step S42), and transmits the LAN registration request (step S43). Then,the communication control part 18 transmits the IP packet of the LANregistration request to the router 3 (step S44). The IP packet of theLAN registration request illustrated in FIG. 29 is transmitted from thePC 1 to the router 3. In the IP packet of the LAN registration request,a destination IP address 131, a sender IP address 132, a destinationport 133, a sender port 134, a message type 135, a terminal ID 136,periodical transmission interval information 137, and optimizationinformation 138. The IP address “100.100.100.1” of the server 2 is setin the destination IP address 131, and the IP address “192.168.10.1” ofthe PC 1 is set in the sender IP address 132. Further, the port “2000”of the server 2 is set in the destination port 133, and the port “1000”of the PC 1 is set in the sender port 134. Further, “LAN registration”is set in the message type 135, “12345” is set in the terminal ID 136,“800 sec” is set in the periodical transmission interval information137, and “YES” is set in the optimization information 138.

In FIG. 27, then, the communication control part 31 of the router 3generates the NAT entry (step S45), and converts the IP address from theprivate IP address form to the global IP address form. Then, thecommunication control part 31 transmits the IP packet of the LANregistration request after the NAT conversion to the server 2 (stepS46). Then, the communication control part 21 of the server 2 receivesthe IP packet of the LAN registration request after the NAT conversion,and transmits the LAN registration request to the NAT control part 22(step S47). The NAT control part 22 performs the LAN registrationrequest reception process (step S48). As illustrated in FIG. 30, in theLAN registration request reception process, the NAT control part 22generates the LAN information table 24 (step S126). Then, the NATcontrol part 22 determines the optimization of the transmission intervalof the LAN registration request (step S127). If “YES” is set inoptimization information of the LAN registration request transmitted bythe PC 1 (see 138 in FIG. 29), the NAT control part 22 transmits a cycleoptimization request to the transmission interval optimization server 7(step S128). On the other hand, if “N/A” is set in optimizationinformation of the LAN registration request transmitted by the PC 1, theNAT control part 22 starts a NAT entry update timer (step S129). Here,the timer value to be measured is a setting value of the periodicaltransmission interval of the LAN information table 24 (see 244 in FIG.13).

In FIG. 27, correspondingly, the communication control part 21 receivesthe cycle optimization request (step S49) from the NAT control part 22to transmit the packet of the cycle optimization request to thetransmission interval optimization server 7 (step S50). In FIG. 31, anexample of information included in the cycle optimization request. TheIP address “100.100.100.2” of the transmission interval optimizationserver 7 is set in the destination IP address 141, and the IP address“100.100.100.1” of the server 2 is set in the sender IP address 142.Arbitrary port numbers used for the communication between the serversare set in the destination port 143 and the sender port 144. Further,“cycle optimization request” is set in the message type 145, and 12345”is set in the terminal ID 146. The IP address “120.120.120.120” of therouter 3 a is set in the terminal IP address 147, and “1200” is set inthe terminal port number 148.

Then, the communication control part 26 transmits the cycle optimizationrequest to the cycle optimization part 25 (step S51). The cycleoptimization part 25 performs a cycle optimization request receptionprocess (step S52). As illustrated in FIG. 32, according to the cycleoptimization request reception process, cycle optimization part 25 sets,in the cycle transmission management table 27, the terminal ID, theterminal IP address, and the terminal port number reported by the cycleoptimization request.

In FIG. 33, as an example of the cycle transmission management table 27,the terminal ID 151, the terminal IP address 152, the terminal portnumber 153, the current cycle 154, and the latest cycle 155. Theterminal ID “12345” of the PC 1 is set in the terminal ID 151, the IPaddress “120.120.120.120” of the router 3 is set in the terminal IPaddress 152. Further, the current cycle is set to the cycle which theserver 2 uses (i.e., the setting value of the periodical transmissioninterval in the LAN information table 24), and the latest cycle is setto “0”.

Under such a situation, the server 2 periodically transmits the NATupdate request packet based on the setting value of the periodicaltransmission interval in the LAN information table 24. The NAT entryupdate process (step S81 through step S85) is described hereinafter.

The transmission interval optimization server 7 performs a NAT entryupdate cycle optimization process (step S53 through step S80),concurrently with the NAT entry update process performed by the server2. Specifically, the cycle optimization part 25 starts counting theperiodical transmission interval with a periodical transmission timer(step S53). When the periodical transmission timer times out, thetransmission interval optimization server 7 performs a NAT entrysurvival confirmation transmission process (step S54). As illustrated inFIG. 34, according to the NAT entry survival confirmation transmissionprocess, when the timer times out (step S134), the cycle optimizationpart 25 transmits a NAT entry survival confirmation to the destinationof the terminal IP address and the terminal port number registered inthe cycle transmission management table 27 (step S135). Correspondingly,the NAT entry survival confirmation is reported to the router 3. Then,the cycle optimization part 25 starts a NAT entry survival confirmationresponse waiting timer (fixed value, 10 sec, etc., for example) (stepS136).

In FIG. 27, correspondingly, the communication control part 26 of thetransmission interval optimization server 7 receives the NAT entrysurvival confirmation from the cycle optimization part 25 (step S55),and transmits the IP address of the NAT entry survival confirmation tothe communication control part 31 (step S56). In FIG. 35, an example ofinformation included in the NAT entry survival confirmation isillustrated. The global IP address “120.120.120.120” is set in thedestination IP address 161, and the IP address “100.100.100.2” of thetransmission interval optimization server 7 is set in the sender IPaddress 162. Further, the global port “1200” is set in the destinationport 163, and the port “2000” of the transmission interval optimizationserver 7 is set in the sender port 164. With respect to the messagecontent, “survival confirmation” is set in the message type 164, and“12345” is set in the terminal ID of the PC 1.

It is noted that the IP address of the NAT entry survival confirmationis an example of a test packet transmitted at a varied interval from thetransmission interval optimization server 7 different from the server 2that transmits the NAT update request packet. According to theembodiment, the test packet is transmitted at the interval thatgradually increases.

The communication control part 31 updates the NAT entry to perform theaddress conversion from the global IP address to the private IP address(step S57). Then, the communication control part 31 transmits the IPpacket of the NAT entry survival confirmation to the PC 1 (step S58).Then, the communication control part 18 of the PC 1 transmits the IPpacket of the NAT entry survival confirmation to the LAN registrationpart 15 (step S59). The LAN registration part 15 performs a NAT entrysurvival confirmation reception process (step S60). As illustrated inFIG. 36, according to the NAT entry survival confirmation receptionprocess, the LAN registration part 15 transmits a NAT entry survivalconfirmation response to the sender of the IP address of the NAT entrysurvival confirmation (step S138). In FIG. 27, correspondingly, thecommunication control part 18 receives the NAT entry survivalconfirmation response transmitted by the LAN registration part 15 (stepS61), and transmits the IP address of the NAT entry survivalconfirmation response to the router 3 (step S62). In FIG. 37, an exampleof information included in the NAT entry survival confirmation responseis illustrated. The transmission interval optimization server 7 which isthe sender of the IP address of the NAT entry survival confirmation isset in the destination IP address 171, and the IP address of the PC 1 isset in the sender IP address 172. “survival confirmation response” isset in the message type 175, and the ID “12345” of the PC 1 is set inthe terminal ID. It is noted that the IP address of the NAT entrysurvival confirmation response is an example of a response packetresponding to the NAT entry survival confirmation.

In FIG. 27, then, the router 3 updates the NAT entry, and performs theaddress conversion from the global IP address to the private IP address(step S63). Then, the communication control part 31 transmits the IPpacket of the NAT entry survival confirmation response to the PC 7 (stepS64). Then, the communication control part 26 of the transmissioninterval optimization server 7 transmits the NAT entry survivalconfirmation response to the cycle optimization part 25 (step S65).

On the other hand, the cycle optimization part 25 starts a responsewaiting timer (step S70) in synchronization with the timing when the NATentry survival confirmation is transmitted in step S55. In FIG. 27, theNAT entry survival confirmation response of step S65 has reached thecycle optimization part 25 before the time-out (see point A in FIG. 27)of the response waiting timer (10 sec, for example). Then, the cycleoptimization part 25 determines that the NAT entry survival confirmationresponse has successfully reached within the response waiting time, andperforms a periodical transmission timer update process (step S71). Asillustrated in FIG. 38, according to the periodical transmission timerupdate process, the cycle optimization part 25 stops the responsewaiting timer (step S140). Then, the cycle optimization part 25 updatesthe cycle transmission management table 27 (step S141). In FIG. 39, anexample of the cycle transmission management table 27 is illustrated. Instep S141, the cycle optimization part 25 copies the timer value (800sec) set in the current interval 184 to the latest interval 185, andupdates the current interval 184 such that the updated timer value(doubled 1600 sec, for example) is longer than the set timer value.

Then, the cycle optimization part 25 returns to step S53 to repeat theprocesses from step S53. In the foregoing, a series of processes in thecase where the NAT entry survival confirmation packet has reached the PC1 is described above in step S53 through step S71. Next, series ofprocesses (step S72 through step S80) in the case where the NAT entrysurvival confirmation packet has not reached the PC 1 is described.

The cycle optimization part 25 starts counting the periodicaltransmission interval with the periodical transmission timer (step S72).The router 3 a deletes the NAT entry due to no communication for thepredetermined time before the time-out of the periodical transmissiontimer (step S73).

When the periodical transmission timer times out, the cycle optimizationpart 25 transmits the NAT entry survival confirmation (step S74), andthe communication control part 26 transmits the IP address thereof tothe router 3 (step S75). Concurrently, the cycle optimization part 25starts the NAT entry survival confirmation response waiting timer (stepS76).

Because the NAT entry has been deleted, the communication control part31 fails the address conversion from the global IP address to theprivate IP address to reject the IP address (step S77). If the responsewaiting timer has timed out without the NAT entry survival confirmationresponse from the PC 1 being received by the transmission intervaloptimization server 7, the cycle optimization part 25 correspondinglyperforms a response timer stop process (step S78). According to theresponse timer stop process illustrated in FIG. 40, when the responsewaiting timer has timed out (step S140), the cycle optimization part 25sets, in a cycle timer 197 of a cycle optimization response illustratedin FIG. 41, the timer value set in the latest interval (see 185 in FIG.39) in the cycle transmission management table 27. The cycleoptimization part 25 transmits the cycle optimization response to theserver 2 (step S141).

In FIG. 27, correspondingly, the cycle optimization part 25 transmitsthe cycle optimization response to the communication control part 26(step S79). The NAT control part 22 receives the IP packet of the cycleoptimization response to perform a cycle optimization response receptionprocess (step S80). As illustrated in FIG. 42, the NAT control part 22sets, in the periodical transmission interval in the LAN informationtable 24, the timer value set in the cycle timer of the cycleoptimization response.

In the NAT update request transmission process, the NAT control part 22sets the periodical transmission interval in the LAN information table24 to the cycle timer of the cycle optimization response, and transmitsthe NAT update request when the cycle timer updated based on the newlyset periodical transmission interval has timed out (step S82). The IPpacket of the NAT update request is transmitted to the router 3 (stepS83), causing the router 3 to update the NAT entry, and after havingbeen subject to the address conversion (step S84), transmitted to the PC1 (step S85).

As described above, the NAT update request packet is transmitted fromthe server 2 to prevent the deletion of the NAT entry upon nocommunication for the predetermined time. For this reason, thetransmission interval optimization server 7 according to the embodimenttransmits the test packets at the transmission interval that graduallyincreases. When the response packet is not returned in response to thetest packet, the transmission interval used immediately before thelatest transmission interval is set to the value of the periodicaltransmission interval. Then, the NAT update request packet istransmitted from the server 2 at the determined periodical interval.With this arrangement, it becomes possible to optimize the periodicaltransmission interval of the NAT update request packet such that theperiodical transmission interval is the longest without causing thedeletion of the NAT entry. As a result of this, it becomes possible toreduce the load of the server 2 as well as traffic of the network.

Third Embodiment

Next, an overall configuration and a function configuration of acommunication system 10 according to a third embodiment of the presentinvention is explained with reference to FIG. 43 and FIG. 44. FIG. 43 isa diagram illustrating the communication system 10 according to thethird embodiment. FIG. 44 is a diagram illustrating a functionconfiguration of a PC 1, a server 2, and a router 3 according to thethird embodiment. The third embodiment differs from the first embodimentin that the LAN that is coupled to the PC 1 is changed from a LAN 1 (LAN11 a) to a LAN 2 (LAN 11 b). Correspondingly, the router 3 is changedfrom a router 3 c to a router 3 d. It is noted that, in FIG. 43, arouter configuration of the router 3 is in a single stage; however, therouter configuration may be in multiple stages.

As illustrated in FIG. 44, a function configuration of the PC 1, therouter 3, and the transmission interval optimization server 7 are thesame as that according to the second embodiment. According to theembodiment, the transmission interval optimization server 7 may beomitted. The server 2 includes a LAN change detection part 28 inaddition to the function configuration (see FIG. 4) according to thefirst embodiment. The LAN change detection part 28 stores, in an overlapmanagement table 29, information of the LAN that is coupled to the PC 1.The LAN change detection part 28 detects, based on the overlapmanagement table 29, a plurality of LANs that are coupled to the same PC1. If the LAN to which the PC 1 is coupled has been changed, the NATcontrol part 22 stops the transmission of the NAT update request packetto the LAN to which the NAT update request packet is transmitted beforethe change.

In the following, a LAN change process is explained with reference toFIG. 45. FIG. 45 is a flowchart of the LAN change process according tothe third embodiment. In FIG. 45, the LAN registration request (LAN1registration request) at the first time is performed, and then the LANregistration requests (LAN2 registration request) at the second time andthereafter is performed. According to the LAN registration requests atthe second time and thereafter, an overlap LAN search process and theLAN change process are performed. It is assumed that the LAN to whichthe PC 1 is initially coupled is LAN1.

The LAN1 registration is described. At first, the UI part 14 of the PC 1transmits the LAN registration request (step S21). The LAN registrationrequest is transmitted to the NAT control part 22 of the server 2 afterhaving been subjected to the address conversion at the router 3 c (stepS2 through step S7). The NAT control part 22 transmits an overlap LANsearch request (step S9). According to the overlap LAN search requestillustrated in FIG. 46, “overlap LAN search request” is set in a messagetype 201, “12345” is set in a terminal ID, “130.130.130.130” is set in aterminal IP address 203, and “1300” is set in a terminal port number.The NAT control part 22 reports the IP address (outward address) and theport number of the IP packet of the received LAN registration request tothe LAN change detection part 28. It is noted that the terminal ID is anexample of identification information of the communication apparatus,and the IP address and the port number of are an example of LANidentification information.

The LAN change detection part 28 performs an overlap LAN search process(step S91). As illustrated in FIG. 47, the LAN change detection part 28determines whether the reported terminal ID exists in the overlapmanagement table 29 (step S151). At that time, the reported terminal IDhas not been registered yet in the overlap management table 29. Thus,the LAN change detection part 28 adds, in the overlap management table29, the terminal ID, the IP address, and the port number that arereported with the overlap LAN search request, and transmits an overlapLAN search response, which includes the search result indicative of nooverlap, to the NAT control part 22. Step S153 illustrated in FIG. 47 isdescribed hereinafter. In FIG. 48, an example is illustrated in whichthe terminal ID, the IP address, and the port number that are reportedwith the overlap LAN search request are registered in a terminal ID 211,a terminal IP address 212, and a terminal port number 213 in the overlapmanagement table 29.

In FIG. 45, the NAT control part 22 receives the overlap LAN searchresponse (step S92). The overlap LAN search response illustrated in FIG.49 includes a message type 221, a result 222 (no overlap, in this case),a terminal ID 223 to which the result is reported, a terminal IP address224, and a terminal port number 225.

In FIG. 45, then, the NAT control part 22 performs the LAN registrationprocess (step S93). According to the LAN registration processillustrated in FIG. 50, the NAT control part 22 determines the result ofthe overlap LAN search response (step S161). If the result is “nooverlap”, the NAT control part 22 registers, in the LAN informationtable 24, the information reported by the LAN registration request (stepS162). Step S163 illustrated in FIG. 50 is described hereinafter. InFIG. 51, an example of the overlap management table 29 stored in the NATcontrol part 22 is illustrated. With respect to the LAN information ofthe LAN to which the PC 1 whose terminal ID 231 is “12345” is coupledto, the router 3 c whose terminal IP address 232 is “130.130.130.130”,the terminal port number 233 “1300”, and the periodical transmissioninterval 234 “800 sec” are registered.

In FIG. 45, after the LAN registration process of step S93, the regulartransmission to the LAN1 is started. Then, as illustrated in FIG. 43, itis assumed the PC 1 is coupled to the LAN2. It is noted that the changein the LAN includes the switching between the wired connection and thewireless connection, etc.

Next, the LAN2 registration is described. According to the LANregistration request after the change in the LAN, the UI part 14 of thePC 1 transmits the LAN registration request (step S94). The LANregistration request is transmitted to the LAN change detection part 28of the server 2 after having been subjected to the address conversion atthe router 3 d (step S95 through step S101).

The LAN change detection part 28 performs the overlap LAN search process(step S102). As illustrated in FIG. 47, the LAN change detection part 28determines whether the reported terminal ID has been registered in theoverlap management table 29 (step S151). In this case, the reportedterminal ID “12345” has been registered in a terminal ID 211 in theoverlap management table 29 illustrated in FIG. 48. Thus, the LAN changedetection part 28 determines that the reported terminal ID has beenregistered in the overlap management table 29 (step S161 in FIG. 50:overlap detected). As a result of this, the LAN change detection part 28overwrites the terminal IP address 212 and the terminal port number 213of the terminal ID 211 “12345” in the overlap management table 29 withthe IP address and the port number reported by the overlap LAN searchrequest (step S163 in FIG. 5). Overwritten overlap management table 29is illustrated in FIG. 52. The entries of the terminal ID 211 “12345”have been overwritten with the terminal IP address “140.140.140.140” andthe terminal port number “1400”.

In FIG. 45, then, the NAT control part 22 transmits the overlap LANsearch response in which the result 222 of the overlap LAN searchresponse illustrated in FIG. 49 is set to “overlap detected” (stepS103). In FIG. 45, then, the NAT control part 22 performs the LANregistration process (step S104). According to the LAN registrationprocess, the information in the overlap management table 29 is stored inthe LAN information table 24 if it is determined in the overlap LANsearch process that the overlap has been detected. In FIG. 53, anexample of the overlap management table 24 stored in the NAT controlpart 22 is illustrated. The entries of the terminal ID “12345” in theLAN information table 24 have been overwritten with the terminal IPaddress “140.140.140.140” and the port number “1400”.

As described above, according to the communication system 10 of thethird embodiment, when the LAN to which the PC 1 is coupled has beenchanged, the server 2 detects the overlapped LAN, which enables theserver 2 to distinguish the currently coupled LAN from previously LAN.

It is noted that the communication system 10 according to the firstthrough third embodiments is suited for a case where service is providedin form of push type communication from the server 2 to the PCs in theprivate network via the Internet.

The communication system 10 according to the first through thirdembodiments prevents the deletion of the NAT entry even if the routerconfiguration of the router 3 is in multiple stages, and enables the NATtraversal. Further, the communication system 10 is applicable to aNAT-capable broad band router that does not comply with UPnP/STUN(Simple Traversal of UDP through NATs). Further, even when the PC 1 isnot in operation, the packet can be transmitted from the server 2 to thePC 1 with the NAT traversal. Further, even if the PC (even in a sleepmode state) is coupled to the Internet via the LAN in which the routerconfiguration is in multiple stages, it becomes possible to keep a statein which the NAT traversal can be performed via the Internet. It isnoted that the communication system 10 according to the first throughthird embodiments is applicable for starting up the PC 1 in the sleepmode with WOL (Wake on LAN) via the Internet when the PC 1 is coupled tothe LAN whose router configuration is multiple stages.

Next, an example of a hardware resource configuration of the PC 1, therouter 3, and the server 2 according to the first through thirdembodiments is explained with reference FIG. 54.

The PC 1 includes a CPU (Central Processing Unit) 601, a ROM (Read OnlyMemory) 602, a RAM (Random Access Memory) 603, an input device 604, anoutput device 605, a HDD (Hard Disk Drive) 606, and a network interface607.

The ROM 602 is a non-volatile semiconductor memory (storage device), andstores therein programs and data such as OS setting, network setting,etc., to be performed at the time of starting up. The RAM 603 is avolatile semiconductor memory (storage) which can temporarily hold theprograms and data. The HDD 606 is a nonvolatile storage which storesprograms and data. The stored programs and data include an OS (OperatingSystem) which is a basic software item for controlling the apparatus asa whole, and application software items for providing various functionson the OS. For example, the HDD 606 stores the programs to be executedby the CPU 601 for the NAT entry update process, the NAT update cycleoptimization process, and the LAN change process. The CPU 601 reads theprograms and date from the storage device described above on the RAM toexecute the processes, thereby implementing control of the apparatus asa whole and installed functions.

The input device 604 includes a keyboard, a mouse or the like, and isused to input operations to the PC 1. The output device 605 includes adisplay, etc., to output or display results, etc., for the user of thePC 1.

The network interface 607 is an interface for coupling the PC 1 to theLAN. In this way, the PC 1 is coupled to the router 3 via the networkinterface 607, and the router 3 performs the address conversion, whichenables the PC 1 to communicate with the server 2 on the Internet.

According to such a hardware resource configuration, the UI part 14 canbe implemented by the input device 604. The LAN registration part 15,the LAN configuration determination part 16, and the UPnP acquisitionpart 17 can be implemented by the CPU 601. The communication controlpart 18 can be implemented by the network interface 607.

The router 3 includes a CPU 701, a RAM 702, a flash memory 703, anetwork interface 704 (LAN), and a network interface 705 (WAN). The CPU701 implements control of the router 3 as a whole and installedfunction, such as the conversion process of the IP address, etc. The RAM702 is a volatile semiconductor memory (storage) which can temporarilyhold the programs and data. The flash memory 703 is an example of anauxiliary storage device.

The network interface 704 (LAN) is an interface for coupling the router3 to the LAN. The router 3 is coupled to the PC 1 via the networkinterface 704.

The network interface 705 (WAN) is an interface for coupling the router3 to the WAN. The router 3 is coupled to the server 2 via the networkinterface 705.

According to such a hardware resource configuration, the UPnP processpart 33 can be implemented by the CPU 601. The NAT table 32 can bestored in the RAM 702 or the flash memory 703. The communication controlpart 31 can be implemented by the network interfaces 704 and 705.

The server 2 includes a CPU 801, a ROM 802, a RAM 803, an input device804, an output device 805, a HDD 806, and a network interface 807. TheCPU 801 implements control of the server 2 as a whole and installedfunction, such as the LAN change process, etc. The ROM 802, the RAM 803,the input device 804, the output device 805, and the HDD 806 are thesame as those of the PC 1, and thus the explanation thereof is omitted.

The network interface 807 is an interface for coupling the server 2 tothe WAN (or the Internet). The server 2 is coupled to the router 3 viathe network interface 705.

The transmission interval optimization server 7 has the same hardwareresource configuration as the server 2, and thus the explanation thereofis omitted.

According to the configuration, the NAT control part 22 and the cycleoptimization part 25 can be implemented by the CPU 801. The LANinformation table 24 and the cycle transmission management table 27 canbe stored in the RAM 803 or the HDD 806. The communication control parts21 and 26 can be implemented by the network interface 807.

It is noted that the PC 1, the server 2, and the transmission intervaloptimization server 7 may include an external I/F (not illustrated) forinterfacing with external apparatuses. The external apparatuses includea recording medium, etc. The PC 1, the server 2, and the transmissioninterval optimization server 7 can read and/or write programs forexecuting the NAT entry update process, the NAT update cycleoptimization process, and the LAN change process from the recordingmedium via the external I/F. The recording medium may be a CD (CompactDisk), a DVD (Digital Versatile Disk), an SD memory card (SD Memorycard), a USB memory (Universal Serial Bus memory), etc.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiment(s) of the presentinventions have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

For example, according to the embodiments, the server 2 and thetransmission interval optimization server 7 are implemented by separateapparatuses; however, the function of the transmission intervaloptimization server 7 may be incorporated into the server 2.

What is claimed is:
 1. A communication apparatus, comprising: aprocessor configured to determine whether a LAN to which thecommunication apparatus is connected has a single-stage routerconfiguration where the communication apparatus is connected to anexternal network via one router or a multiple-stage router configurationwhere the communication apparatus is connected to the external networkvia multiple routers, the communication apparatus being connected to aserver via the LAN and the external network; and request the server totransmit a NAT update request packet to one of the routers, which isregistered in the server and performs NAT traversal to enable thecommunication apparatus to communicate with the server, in response todetermining that the LAN has the multiple-stage router configuration. 2.The communication apparatus of claim 1, wherein the processor is furtherconfigured to transmit a response packet to the server in response to atest packet transmitted from the server with a varied interval; and atransmission interval at which the NAT update request packet istransmitted from the server to the one of the routers is determinedaccording to a presence or absence of a reception of the response packetby the server within a response period.
 3. A server that is coupled to acommunication apparatus on a LAN via an external network involving a NATtraversal with a router of the LAN, the server comprising: a storageconfigured to store identification information of the communicationapparatus and identification information of the LAN obtained when theserver is coupled to the communication apparatus on the LAN; and aprocessing device, wherein the processing device is configured todetect, based on the identification information of the communicationapparatus and the identification information of the LAN, a change in theLAN to which the communication apparatus is coupled; and transmit a NATupdate request packet to the changed LAN whose change has been detected,in response to a request from the communication apparatus to transmitthe NAT update request packet to the router which is registered in theserver and performs the NAT traversal.
 4. The server of claim 3, whereinthe processing device is further configured to determine a transmissioninterval of the NAT update request packet based on a presence or absenceof a reception of a response packet within a response period, theresponse packet being transmitted from the communication apparatus inresponse to a test packet transmitted with a varied interval, andtransmit the NAT update request packet at the determined transmissioninterval.
 5. A communication system, comprising: a server; and acommunication apparatus connected via a LAN and an external network tothe server, wherein the communication apparatus is configured to:determine whether the LAN has a single-stage router configuration wherethe communication apparatus is connected to the external network via onerouter or a multiple-stage router configuration where the communicationapparatus is connected to the external network via multiple routers, andtransmit a request requesting the server to transmit a NAT updaterequest packet to one of the routers, which is registered in the serverand performs NAT traversal to enable the communication apparatus tocommunicate with the server, in response to determining that the LAN hasthe multiple-stage router configuration; and the server is configured totransmit the NAT update request packet to the one of the routers inresponse to the request from the communication apparatus.
 6. Thecommunication system of claim 5, wherein the communication apparatus isfurther configured to transmit a response packet to the server inresponse to a test packet transmitted from the server with a variedinterval; and the server is further configured to determine atransmission interval of the NAT update request packet based on apresence or absence of a reception of the response packet within aresponse period, and transmit the NAT update request packet to the oneof the routers at the determined transmission interval.
 7. Thecommunication system of claim 5, wherein the server includes a storageconfigured to store identification information of the communicationapparatus and identification information of the LAN obtained when theserver is connected to the communication apparatus; and the server isconfigured to: detect, based on the identification information of thecommunication apparatus and the identification information of the LAN, achange in the LAN to which the communication apparatus is connected; andtransmit the NAT update request packet to the one of the routers relatedto the changed LAN whose change has been detected.
 8. A communicationmethod executed by a computer in a communication apparatus, thecommunication method comprising: determining whether a LAN to which thecommunication apparatus is connected has a single-stage routerconfiguration where the communication apparatus is connected to anexternal network via one router or a multiple-stage router configurationwhere the communication apparatus is connected to the external networkvia multiple routers, the communication apparatus being connected to aserver via the LAN and the external network; and requesting the serverto transmit a NAT update request packet to one of the routers, which isregistered in the server and performs NAT traversal to enable thecommunication apparatus to communicate with the server in response todetermining that the LAN has the multiple-stage router configuration. 9.The communication method of claim 8, further comprising: transmitting aresponse packet in response to a test packet transmitted from the serverwith a varied interval; causing the server to determine a transmissioninterval of the NAT update request packet based on a presence or absenceof a reception of the response packet within a response period; andcausing the server to transmit the NAT update request packet to the oneof the routers at the determined transmission interval.